The invention relates to flexibly deformable holding elements for substrates. In this respect, the substrates can be held in a fixed manner at a surface of the holding element electrostatically or also by means of negative pressure. A use of the invention is in particular possible in the processing of semiconductor components or in the manufacture of micromechanical elements. In this respect, plate-shaped substrates such as preferably wafers or masks can be transported and held in a defined position with the help of the holding elements.
Electrostatic holding elements or also so-called vacuum holding elements, which are usually also called chucks, are known per se. However, the demands on the positioning precision and its observation have increased in the processing and due to miniaturization. In the meantime, electromagnetic radiation of extremely small wavelength is used for photolithographic processes, whereby these demands have been further increased.
A wafer to be processed therefore has to be held in an exact position, with this being the case, for example, with respect to masks used in a lithographic processing. Even slight spacing deviations of the substrate surface with respect to a mask have a very negative effect here which can be caused e.g. by planarity errors/planarity deviations at the respective substrate surface. The substrates in question frequently have a small thickness so that deflections occur due to manufacture. Thickness deviations or deformations can also arise due to particles which have to be taken into account. Substrates can be deflected due to uneven surfaces, which leads to distortion in the lithographic exposure. Metric errors, structural defects and ultimately defective microelectronic components can thereby be obtained which result in rejects.
As is known, sensors are used to detect such deviations. Their measured signals are also utilized to effect a direct deformation of a holding element and of a substrate held thereby. Different physical or mechanical mechanisms of action are used for this purpose.
It is thus known from WO 01/90820 A1 to form a structured piezoelectric layer at the surface of a holding element on which a carrier layer is formed on which a wafer can be placed and held as a substrate. However, an influencing of the shape of a substrate placed there can only be carried out with limitations due to the structuring at the surface of such a holding element. Deformations can occur which cause strains in the substrates or steps at the surface. The effort and/or cost for the control and the manufacture are very high.
This also applies analogously to other examples such as are known from EP 0 077 878 B1 or from U.S. Pat. No. 5,563,684. Individual adjustment elements are used there which are aligned perpendicular to the surface on which the substrate has been placed and whose lengths can each be modified individually. The surface contour of the holding element is thereby selectively changed.